1. Field of the Invention
The present invention relates to an image forming apparatus including a plurality of fixing units, a control method for an image forming apparatus, and a program.
2. Description of the Related Art
In an image forming apparatus, an unfixed image drawn normally with toner on a material is fixed to a surface of the material by heating it under pressure in a fixer. Such a fixer is heated by an internal heater, and it is controlled such that the amount of heat taken away by a material passing therethrough could be compensated to keep the temperature necessary for fixing.
An increased number of types of material to be conveyed through an image forming apparatus are available yearly. However, it may be difficult for an image forming apparatus configured to perform image fixing with one fixer to provide all of stable fixability, image quality of fixed images and productivity on all types of material. In order to address this and in order to avoid problems such as shortage of a heat amount due to such a configuration with one fixer, a plurality of fixers may be serially connected in a conveying path (as disclosed in Japanese Patent Laid-Open Nos. 06-348159 and 07-271226).
A method has also been disclosed (in Japanese Patent Laid-Open No. 2007-199597) in which when a predetermined fixer is not available, the processing speed for fixing may be reduced so that the fixing process may be performed by the other fixers only.
In an image forming apparatus having a plurality of fixers, keeping the temperatures of the plurality of fixers may consume a large amount of power. Normally, one fixer may be used for the most frequently used normal sheet, for example. Keeping the temperatures of a plurality of fixers is necessary for less frequently used materials, which unnecessarily consume power.
Even temperatures of a plurality of fixers that are kept as described above must be further increased to a temperature required for performing a fixing process, which further consumes power. Use of a plurality of fixers for printing a few sheets may consume more power than printing them with one fixer, which is also disadvantageous in terms of the printing performance.